Inks containing florescent pigments are often used to enhance or alter the observed colors of printed images. The fluorescent inks are excited when illuminated with specific wavelengths, (most often out of the ultraviolet “UV”) spectrum, and may exhibit increased brightness and saturation compared to the reflection of standard cyan, magenta, yellow, and key (black) “CMYK” or cyan, magenta, and yellow “CMY” inks. When normal visible illumination conditions are applied, fluorescent inks can have a variety of different appearances such as transparent, diffuse white, or colored depending on the manufacturing process, and chemical components. Because of the wide range of color-alteration or enhancing effects, prints containing florescent inks are widely used in many fields including art, entertainment as well as optical documents security.
UV prints are typically limited to effects such as enhancing already printed colors (e.g., making the colors brighter and more vivid such as when saturated under UV light), or to reveal hidden images. However, when used to reveal hidden images, the intensity of the colors strongly depends on the type of print surface used. For example, when invisible florescent inks are printed onto a surface covered with black ink, the output will be much darker than compared to when printing the same florescent inks onto a white surface, i.e., surface without black ink. In short, the intensity of emitted light from the UV inks (e.g., RGB UV) is reduced when visible inks (e.g., CMY) are printed below since the RGB UV light is reflected from the CMY inks. The reduced emission efficiency can prevent prints having a complete change between two unrelated images under different illumination settings, since the weak color alteration effect leads to an undesired visibility of the CMY ink under UV illumination.